Flexible risers are commonly used in offshore oil and gas installations to connect surface and subsea facilities. The flexible riser is either a flexible pipe or an umbilical. Flexible risers (which also may be referred to herein as flexible pipes) convey hydrocarbons and ancillary fluids, and conventionally have a multilayered construction. The layers include fluid barriers, helical armoring, anti-wear, and specialized layers that depend on the application (e.g. thermal insulation). An umbilical houses control lines that supply power, communications, fluid injection or lift and normally include armoring layers. Flexible refers to compliant bending whilst the axial and torsional stiffness is comparatively high.
FIG. 1 shows exemplary flexible riser 102 configurations 104-114 between offshore surface and subsea facilities. The riser 102 is compliant in bending which is a key advantage of flexible riser constructions. The riser design requires careful assessment of the bending in cases of extreme and fatigue loading, which may cause radial bending of up to 5 meters (16.5 feet) or more. Design procedures are available for this purpose. In-situ monitoring can have a key role in design critical applications (extreme or fatigue) where the safety of the design requires surveillance data to confirm its validation or evidence to support remedial action.
The location of the bend sensitive locations is dependent on the riser configuration and environmental loading from external and internal sources. These locations may include interface zones (e.g., a connection point, wherein a hard interface includes a point where the load is transferred from one structure to another, etc.) with surface (topside) and subsea structures, hog and sag bends (e.g., wherein a hog bend is a hump like bend or the opposite of a sag bend) and adjacent sections of the riser 102. The flexible riser 102 is normally supported with a bend stiffener (e.g., a tapered section that limits the bending of a flexible riser) or rigid bellmouth (e.g., a curved section for guiding the flexible riser along a stiff predefined curve) in the interface zones. Other bend limiter devices are also available in less onerous applications. However, bend stiffeners, and the like, are designed to last a certain number of years based on numerical modeling, but not on actual monitoring of bends. As such, the design life of flexible risers with bend stiffeners, when engineered, is typically conservative, and the actual monitoring of bending stress can be used to extend the life of flexible risers with bend stiffeners and other bend limiter devices. Therefore, there is a need to extend the life of flexible risers, bend stiffeners, and the like.